The body of work proposed n this fellowship is aimed at gaining a greater understanding of mamalian forebrain development. In particular, the role of the secreted signaling molecule Sonic Hedgehog in early forebrain patterning will be explored. In the first specific aim, the Sonic Hedgehog signaling pathway will be studied to determine if secondary signaling pathways are activated simultaneously. The second specific aim will address the role of Sonic Hedgehog in early (<E9) patterning of the mouse telencephalon. The third aim will examine the possible involvement of other signaling pathways in determining the outcome of Sonic Hedgehog signaling. This work will hopefully lead to a deeper understanding of regional specification in the developing forebrain.